This protocol includes the general screening procedure for all volunteers who apply to serve as subjects in one of the numerous studies of cocaine abuse by Drs. Marian Fischman and Richard Foltin and their colleagues. Subjects include non-treatment seeking users of intravenous and smoked cocaine and also non-drug abusing normal controls. The screening, which can require up to five visits per subject, includes medical and psychiatric tests, blood and urine tests, pregnancy tests (for female participants), and chest x-rays. Until early 1999, this protocol also included a small number of inpatient admissions for studies of cocaine abstenance.